Solid jet or rocket fuel



United States The invention is particularly useful in providing a fuelcomprising for example a mixture of powdered carbonaceous material suchas coal, charcoal or the like and powdered metals which are ofrelatively low molecular weight and burn easily and quickly to producehigh temperatures and high velocity gases.

It is a principal objectof the invention to provide a catalyzed powderedmixture which forms a suitable fuel for jet airplane engines, gasturbines, rockets, missiles, propellants, power plants, and as utilizedin the fields of aviation, rail transportation, agriculturaldistribution systems for fertilizer and insecticides, destruction ofvegetation, and as may be useful for military purposes, as for exampleflame throwers, fire bombs, etc.

It is another object of the invention to provide a composition useful asfeul, explosive products or as ignition catalysts for initiating andpromoting high temperature reactions and the production of high velocityhot gases.

It is another object of the invention to provide a combustiblecomposition which has very short flame propulsion area and whichexhibits an accelerated rate of combustion due to the highly pyrophoriccharacter of the fuel mixture.

It is another object of the invention to provide a powdered fuel mixturewhich may be used in the form of a slurryand containing auto-oxidationcatalyst dispersed in a liquid hydrocarbon, and which produces a largeamount of exothermic heat during combustion.

A still further object of the invention is to provide a method foraccelerating the combustion of powdered combustible substances wherebythe flame spreads through the mass of fuel and brings about theexploding and rapid disintegration of each of the powdered particles andthe propagation of high velocity combustion gases. The powdered fuelmixture of the invention is characterized by exhibiting a high flamespeed during combustion and the production of a high pressure area. Byutilizing a suitable mixture of coal dust, metal dust, and autooxidation catalysts, and dispersing the same while introducing asufl'icient supply of air or oxygen, and preferably in the form ofliquid ozone, maximum evolution of heat is obtained during combustion ofthe dust.

In accordance with the invention, a basic process is provided forobtaining high temperatures of combustion and the production of highexhaust velocity gases for propulsion purposes. The invention will bedescribed more particularly with reference to the use of mixtures ofpowdered coals and powdered metals, e.g., aluminum and magnesium,however, other combustible powdered carbon and metals of similar naturemay be used or admixed therewith to provide an improved fuel.

In preparing the fuel mixture powdered metal material, especially metalsof low atomic weight, for example aluminum, magnesium, beryllium, aremixed with powdered coal or carbonaceous material and a catalysts suchas a metallic soap. The particle size of the metal is generally on theorder of 20 microns or less and preferably a micron or less in diameter.The particle size of the coal or carbonaceous material is generally lessthan 1000 microns and preferably substantially in the same particle sizerange as the metal powder. The mixture of coal dust, metal dust andmetallic soap may be used as a dry powder fuel or admixed with liquidhydrocarbon to form a slurry.

The proportionate amount of coal or charcoal dust and atent 3,032,451Patented May I, 1962 metal powder employed may, of course, be varieddepending upon the metal powder used as well as the kind of coal dustemployed and the particular use to which the fuel is to be put. For mostpurposes, the amount of powdered metal present may range between about1% and 35% by weight of the powdered mixture of coal dust and metalpowder. Since the cost of powdered metal is relatively high as comparedto powdered coal, the metal powder is used more sparingly.

To catalyze and enhance the combustion rate of the powdered fuel mixtureand produce a high temperature reaction, there is introduced a smallamount of a metallic soap or mixture of such metallic soaps, for example0.1 to 5% by weight of the powdered metal constituents comprises ametallic soap such as a stearate, palmitate, oleate, ricinoleate, etc.,of aluminum, magnesium, beryllium, titanium, zirconium, tin or the likewhich exhibit auto oxidation catalytic properties. The metal particlesof the fuel mixture are in the form of dust or flakes, with metallicsoap being preferably coated on or admixed with the flakes of metal,e.g., aluminum metal flakes coated with aluminum stearate mixed withcoal dust forms an excellent fuel mixture.

Where the fuel is to be employed as a liquid, the carbonaceous and metalparticles in the form of flakes or dust and metallic soap catalyst aredispersed in a liquid hydrocarbon, for example kerosene, gasoline,diesel oil, etc., to provide a liquid combustible carrier for thepowdered metalmaterials. Such a fuel is useful for operating jetengines, rockets and high temperature operated prime movers, and wherethe maximum B.t.u.s are to be extracted from the burning fuel in apredetermined time.

For promoting the oxidation and increasing the speed of burning of thefuel, a peroxide such as hydrogen or benzyl peroxide, etc. may beintroduced into the fuel mixture initially or during the burning of thesame. For this purpose 0.5 to 2% by weight of the fuel solids maycomprise a peroxide.

As specific examples of the improved powdered metal fuel of thisinvention a mixture of powdered coal, aluminum metal dust, preferably aspowdered metal foil of a particle fineness of an average size of onemicron is coated with aluminum stearate (0.1 to 5% by weight of thepowdered metal mixture). In place of aluminum metal other low atomicweight metals such as beryllium and magnesium, or suitable mixturesthereof may be used. Small amounts up to 1% of other combustible metals,e.g., titanium metal powder, zirconium, zinc or tin may be present.

The metallic soap utilized as auto oxidation catalysts are preferablysalts of metals in groups II, III and IV of the periodic table,representatives of which are the stearates or palmitates of aluminum,magnesium, titanium, zirconium and tin.

The powdered fuel mixture of coal dust and metal powder may be used inthe form of a slurry, the same being admixed with liquid hydrocarbon anddischarged into a combustion chamber. This slurry of oil and dustparticles may be sprayed into a combustion chamber of the engine andmixed with air or oxygen, preferably as liquid ozone, and burned. Ingeneraly', one to twenty-five parts of the solid fuel constituents toparts by weight of the liquid hydrocarbon provides a suitable liquidfuel mixture. Liquid ozone in amount of 0.1 to 1% by weight of the totalfuel mixture may be used. The burning of the fuel with ozone increasesthe exhaust velocity substantially over the use of air or oxygen alone.Higher or lower proportionate amounts of the liquid hydrocarbon andpowdered fuel constituents may be employed as needed, to provide a fuelhaving the requisite consistency and burning characteristics desired.The powdered fuel may be mixed with the liquid hydrocarbon either beforeor during burning of the mixture.

The presence of the auto-oxidation catalyst in suflicient amount tocatalyze the reaction forms an essential con stituent of the powderedfuel. The metal particles which are combustible and tend to vaporizereadily produce a high temperature reaction during the combustion.Powdered aluminum metal, for example, produces a flame having atemperature of 3500 C. or higher. The very high temperatures producedduring the catalyzed reaction causes the powdered coal and metalparticles to be rapidly disintegrated and vaporized. The combustion ofthe metal and coal particles thus proceed at a high rate, thetemperature and explosive action being enhanced by the catalytic actionof the metallic soap. The high temperatures produced combined with theviolent disintegration and vaporization of the powdered fuel particlesis believed to account for the unexpected high calorific valuesproduced.

Heretofore, in the combustion of solid fuel particles, the maximumB.t.u.s have not been obtained principally because the initial heatingof the particles did not result in the production of temperatures highenough to disintegrate and vaporize the particles and permit air oroxygen to come in contact with all the particles and support itscombustion to completion. In other words, under conventional combustionreactions using powdered metals there was always a certain minimumamount of the particles which were not burned to completion but passedoff as smoke.

By utilizing a mixture of powdered metal, powdered coal or the likecarbonaceous material and auto oxidation catalyst admixed with oxygenand burned in the combustion chamber, there is produced high temperatureand high velocity gases for operating the jet engine. The proportionateamount of fuel used is controlled so as to produce the most eflicientoperation of the engine.

The production of high temperatures during the combustion results in themaximum extraction of B.t.u.s from the powdered coal and powdered metalmaterial. To achieve this, however, it is requisite that the reaction beconducted so that the boiling point or vaporization point of thecombustible material is lower than the flame temperature, and that theheat of vaporization is lower than the energy required to initiate rapidsurface oxidation or combustion.

The catalytic action of metallic soaps facilitates the burning of themetal dust and provides a high temperature reaction so that the'maximumB.t.u.s are obtained from the solid fuel particles. During combustion ofthe fuel the high temperatures produced rapidly transform the metalparticles into gases at high temperatures.

Further, the use of pyrophoric metal powders, for example of aluminum,magnesium and beryllium together with coal dust, when used with apetroleum hydrocarbon carrier such as gasoline, kerosene, diesel oil orthe like provides a fuel which is more sensitive to ignition and a fuelmixture wherein the flame produced by combustion proceeds more rapidlythrough the fuel, than when the dust particles are employed alone. yMoreover, the high temperature gases formed by the combustion of themixture results in the production of high velocity exhaust gases.

In addition to the high'rate' of'rea'ction and production of hightemperatures and high gas velocities during combustion of metal dust andcoal particles, it has been found that the addition of a small amount ofa metallic soap such'as aforementioned, for example aluminum, magnesiumstearate or oleate or the like, will further accelerate this ignitionand flame propagation during combustion of the fuel. This is probablydue'to the fact that the porous surface of the particles adsorb gas fromthe surrounding atmosphere and the metallic soap catalyzes the reaction.

To control the combustion and prevent explosion and to facilitatecombustion an excess of oxygen in the atmosphere is preferred and isintroduced into the fuel either from a liquid ozone or mixture of airand peroxide, as heretofore explained. In this manner it is possible toproduce the combustion at a lower ignition temperature and increase therate of combustion and the adsorption of oxygen on the dust particles.

Metal particles such as aluminum, magnesium, beryllium and the likecombustible material in the form of dust ignited in the presence ofmetallic soap catalytic agent burns at a high rate and temperature. Thecombustion rate promoting catalysts produce a powdered metal fuel whichhas a lower explosive limit or temperature, particularly in the presenceof methane, oxygen or air, and results in the enhancement of thecombustion of the fuel.

Control of the combustion and explosive properties of the powdered fuelmixture can be effected by utilizing different oxidizing agents and invarious proportions. In this manner the incendiary action of the fuelmay be controlled so as to either accelerate the combustion or burningup of the fuel particles or slow down their combustion as may berequired in the use of the fuel. Thus, for making a fuel useful ininternal combustion engines utilizing powdered carbon such as coal dustand metal powder, the combustion may be speeded up by the use ofmetallic soap and peroxide catalysts so that the mixture will burn andprovide the high temperature reaction gases necessary to propel thepiston in a predetermined time. In other instances where the fuel isrequired to burn more slowly, the use of negative catalysts such asthose which do not accelerate the combustion but tend to decelerate thecombustion are incorporated in the fuel.

In the case of metal dust such as aluminum dust and similar metal dust,the ignition of the same is believed to have an electric or electronicorigin as opposed to thermal ignition. The electrical discharges orionization is believed to produce ozone and aluminum oxide (A1 0 whichreacts with the fine dust particles and initiates the decomposition ofthe same and flame propagation during the combustion of the fuel.

The electrical ignition depends largely upon the production of asufiicient concentration of charged particles and which results fromelectronic collisions due to ionization of the materials or the presenceof ions or ionzed particles in the explosive-mixture. This electronicphase of the combustion is believed to play an important roll in theincreased efiiciency of the fuel of this invention. The same issubstantially true in the case of thermal ignition.

It is also considered to be immaterial whether the theory ofpredistillation of dust during ignition and combustion takes place orwhether such a theory may be used to explain what happens to the fuelduring combustion, or whether it involves some other theory for theproduction of the improved results. In the case of the predistillationtheory of dust ignition, it is believed that all dust ignition involvespurely a gas or vapor explosion and that the energy of the ignitionsource provides heat to decompose the dust particles thus causing theevolution of the volatile matter. In this manner-the volatilized gassyparticles mix more readily with air and ignite and the combustionproceeds at a high rate and the heat produced in turn further heats andvolatilizes other particles not yet volatilized.

One of the objections made to the above theory has been that theignition temperature of some dust, including' coal, are lower than theignition temperatures of the gases involved such as methane or the likehydrocarbon. However, there seems to be some support for the theory thatduring the initial heating and combustion of the dust there is notenough air present at thc'surface of the particle to continue to supportthe combustion, and

consequently the temperature rises above the ignition point of the solidcausing it to distill and eventually to ignite, thus initiating thecombustion reaction.

In the preferred process of carrying out of the combustion of the novelfuel of this invention, it is sought to have the concentration such aswill provide sufficient heat to produce complete oxidization of thecombustible coal and metal dust particles and thus release the maximumB.t.u.s. The heat produced by complete oxidization of a portion of thedust particles in the available oxygen is enough to heat the rest of thedust in the mixture to bring the same to the ignition temperature.Theoretically, neglecting disassociation, the strongest explosion orgreatest explosive force should be produced at a concentrationcorresponding to stoichiometric weight mixtures of the fuel ingredients.This can be computed if the chemical composition of the dust is knownand provided complete combustion of the material is assumed to takeplace. In practice, however, somewhat richer dust mixtures are found tobe the most explosive.

The adjustment of these mixtures to provide the greatest heat productionis facilitated by the catalytic action of the metal powder constituenttogether with the auto-oxidation catalyst, and the fluid carrier whichis preferably hydrocarbon as described. The initial temperature,pressure, oxygen, content, humidity, specific heat and heat conductivityof the atmosphere all are factors which influence the dust explosion.The presence of oxygen is, of course, a most important factor.

As a source of ignition it is preferred to utilize a flame or hotsurface. The presence of moisture which normally is a constituent of themixture is advantageous since it reacts with the metal powder andsimilar mate rials at the reaction temperatures and results in theevolution of hydrogen gas. The production of hydrogen gas is effectedparticularly at elevated temperatures wherein decomposition andionization of moisture is produced. This reduces the surface oxidecoating which would otherwise tend to form on the particles and thusmakes the fuel mixture highly sensitive to ignition and combustion.

Other pyrophoric metal dust particles may be present such as finelydivided metal powders of iron, manganese, copper, uranium, nickel,zirconium and others, metal oxides, hydrides, carbid3s, nitrides andmetal alloys which also oxidize rapidly on exposure to air that theytend to heat and ignite. While there is no apparent agreement regardingthe exact mechanism of the pyrophoric ignition, it is believed that theprocess varies somewhat with the type of dust, its fineness and surfacecharacter.

The basic discovery in this invention is that by utilizing a combinationof combustible metal dust with coal dust that the combustion can beachieved and controlled whereby the maximum liberation of gas and heatresults from the reaction. The pyrophoricity of these dusts, ashereinbefore mentioned, is believed to be relaed to a metastableinternal equilibrium in the powders. Thus, one of the advantages ofutilizing these dusts of pyrophoric character, such as aluminum and/ormagnesium or beryllium metal dusts, is that with a sufiicient dispersionof these extremely fine particles, the same will self-ignite by anelectrostatic spark discharge within the cloud of dust.

Particularly satisfactory results have been secured with dust samples offiner than ZOO-mesh. This fuel can be passed through an electricallyheated cylindrical alundumcore furnace construction for ignition. Theignition temperatures for the dust will range from about 200 C. to morethan 1000 C. These figures depend upon the dispzrsibility, fineness,uniformity of the dust, the ignition source, the timing of ignition andthe interpretation,

of what constitutes limiting flame propagation.

The igniting energy of these dust clouds may vary with the fineness, themoisture content and somewhat with the concentration in the cloud. Forinstance, undispersed layers of beryllium metal powder have been ignitedby sparks of less than 1 microjoule (1 muj.) energy while other duststake considerably stronger sparks. The igniting energy of dust clouds inair ranges from about 10 millijoules (10 mi.) to several joules.

The igniting source generally preferred is a high voltage inductionspark. When these dusts are thus ignited the pressure is developed tomore than 1b./in. and rises to an average rate of pressure of about 5000lb./in. per second and the maximum rates to more than 10,000 lb./in. persecond. When using a high voltage continuous induction spark anddispersing the dust through a furnace at 850 C. a satisfactory resultcan be secured.

The minimum concentration of coal dust that will propagage large-scaleexplosions is approximately 50 mg./liter (0.05 oz./ft. of air. Pressureis nearly 150 lb./in. and flame velocities in excess of 6-000 ft./sec.have been accomplished by the employment of the thermal properties ofthe metal dust and the catalysts, e.g., aluminum flakes and similarother dusts. As hereinbefore stated, in the presence of a liquidhydrocarbon fuel and oxygen, it is possible to achieve temperature andgas velocities of great magnitude and by adjusting the fineness of thematerials involved, the amount of moisture present and the oxygen, themaximum energy can be released.

It will thus be seen that the present invention provides a novel fueland method of producing high temperature combustion reactions, andwherein metal dust particles form a principal constituent.

Further, the invention provides a fuel wherein a catalyzed metal dust isutilized to produce a high temperature fuel and wherein the maximumB.t.u. values are obtained.

It is understood that various changes and additions may be made incompounding the fuel of this invenion and that the proportionate amountof ingredients may be varied over a relatively wide range, dependingupon the particular use to which the fuel is to be put. Such changes andvariations are con emplated to come within the spirit and scope of thisinvention, and which are more particulary s t forth in the append:dclaims.

What is claimed is:

1. A fuel mixture consisting essentially of particles of coal, particlesof metal and a catalys for promoting the burning of the fuel mixture,the particles of coal constituting the principal constituent and saidmetal particles constituting from 1% to 35% by weight of the mixture ofcoal and metal particles, said metal particles being selected from thegroup consisting of aluminum, magnesium and beryllium, said catalystconsisting of a fatty acid salt of a metal selected from the groupconsisting of aluminum, magnesium, titanium, zirconium and tin, and saidfatty acid metal salt constituting from 0.1% to 5% by weight of themetal particles and the balance of the fuel mixture being composed ofparticles of coal.

2. A fuel mixture consisting essentially of the combination of powderedsolid constituents and a catalyst for promoting the burning of the fuelmixture, said solids consisting essentially of particles of coal whichconstitutes the principal constituent, particles of metal and a catalystconsisting of fatty acid salt of a metal selected from the groupconsisting of aluminum, magnesium, titanium, zirconium and tin, saidmetal particles constituting from 1%to 35% by weight of the mixture ofcoal and metal particles, and said catalyst consisting.

of 0.1% to 5% by weight of said metal particles of the fuel mixture andthe balance of the fuel mixture being composed of particles of coal.

3. A fuel mixture consisting essentially of particles of coal whichconstitutes the principal constituent, particles of metal and a catalystfor promoting the burning of the fuel mixture, said metal particlesconsisting of aluminum metal and which is present in an amount betweenabout 1% and 35% by weight of the mixture of coal particles and metalparticles, and aluminum stearate t catalyze the burning of the fuelmixture, and said catalyst consisting of 0.1% to 5% by weight of saidmetal particles of the fuel mixture and the balance of the fuel mixturebeing composed of particles of coal.

References Cited in the file of this patent UNITED STATES PATENTS ONeilAug. 26, 1924 Pearsall Feb. 25, 1947 Van Loenen Nov. 21, 1950 Bartlesonet a1. July 17, 1951 Clay et al. Nov. 13, 1951

1. A FUEL MIXTURE CONSISTING ESSENTIALLY OF PARTICLES OF COAL, PARTICLESOF METAL AND A CATALYST: FOR PROMOTING THE BURNING OF THE FUEL MIXTURE,THE PARTICLES OF COAL CONSTITUTING THE PRINCIPAL CONSTITUENT AND SAIDMETAL PARTICLES CONSTITUTING FRROM 1% TO 35% BY WEIGHT OF THE MIXTURE OFCOAL AND METAL PARTICLES, SAID METAL PARTICLES BEING SELECTED FROM THEGROUP CONSISTING OF ALUMINUM, MAGNESIUM AND BERYLLIUM, SAID CATALYSTCONSISTING OF A FATTY ACID SALT OF A METAL SELECTED FROM THE GROUPCONSISTING OF ALUMINUM, MAGNESIUM, TITANIUM, ZIRCONIUM AND TIN, AND SAIDFATTY ACID METAL SALT CONSTITUTING FROM 0.1% TO 5% BY WEIGHT OF THEMETAL PARTICLES AND THE BALANCE OF THE FUEL MIXTURE BEING COMPOSED OFPARTICLES OF COAL.